Spray devices including a sonotrode have already been proposed. By way of example, U.S. Pat. No. 3,970,250 and European patent applications Nos. EP 0 389 665 and EP 1 508 382 A1 disclose spray heads having composition feed channels passing therethrough that are of constant cross-section, and that open out to the front face of an end collar of the sonotrode, said front face defining the ejection surface.
In U.S. Pat. No. 3,970,250, the sonotrode has a frustoconical portion that connects directly with the end collar. The sonotrode is placed inside a nozzle for blowing air, being set back from the opening through which air leaves the nozzle. The sonotrode is fastened via a vibration node of the frustoconical portion. The nozzle has a converging portion that passes close to the free edge of the collar, thereby reducing the flow section available to the air stream and, according to that patent, preventing the composition from flowing over the rear face of the collar.
Application No. EP 0 389 665 A1 discloses a shutter disposed in such a manner that in the absence of spraying, it closes the orifice through which the composition feed channel opens out into the ejection surface. The shutter is controlled by a rod that passes through the sonotrode via the feed channel. Such a device is of relatively complex construction and may result in added time and cost.
In application No. EP 1 508 382 A1, an end collar is pierced by multiple orifices for passing an air stream for entraining particles of a composition. Composition feed takes place by bringing the composition directly onto the ejection surface via a duct external to the sonotrode.
EP 0 569 611 A1 discloses a spray device including a peristaltic pump for bringing the composition onto the ejection surface.
Application WO 2007/104859 A1 discloses a device in which the composition is brought into contact with the ejection surface by a capillary wick. The sonotrode includes an end collar that is connected to a circularly-cylindrical portion. The use of a capillary wick may not enable compositions that are relatively viscous to be sprayed. The collar may not bend under the effect of the sonotrode vibrating.
FR 2 747 542 discloses a hair dryer arranged to spray a mist of fine water droplets in order to humidify the hair.
FR 2 532 861 describes an ultrasound sprayer for operating at a frequency of about 60 kilohertz (kHz), in particular for a fuel oil burner. The thickness of the end collar is about 1 millimeter (mm) for a diameter of about 12 mm.
U.S. Pat. No. 4,541,564 discloses a high flow rate spray device. The thickness of the end collar is about 3 mm for a diameter about 5 centimeters (cm), thereby making the spray device relatively bulky.
U.S. Pat. No. 3,904,896 discloses a spray device having an end plate with a diameter of 10 mm for a thickness of 1 mm.
Therefore, it is desirable to overcome one or more of the disadvantages of the prior art with a sprayer which meets one or more of the following desires:                firstly the spray should be precise and as uniform as possible so as to facilitate the spraying operation and, where desired, so as to enable makeup to be applied regularly. In particular, it may be found desirable for the spot formed by the sprayed composition to have limited or no marked central void, associated with the presence of the sonotrode in the vector air stream;        the size of the spray droplets should substantially satisfy health standards, minimizing fine droplets;        the flow rate of the composition should be sufficient to ensure that the spraying operation is not too lengthy and/or uncomfortable;        the spray device should be capable of adapting to compositions presenting viscosities that may vary with varying formulations;        the device should be ergonomic, with sufficient operating lifetime, easy to handle, and reliable;        the spray head should not clog easily and, where appropriate the spray should, need be easy to clean;        operation should take place without the device clogging without an excessive and undesired accumulation of composition in zones of the device; and        the cost of the device should remain compatible with mass distribution to the public.        